Dain pineapple and put juice in a saucepan.
Add eggs, sugar, flour, and beat together with pineapple juice.
Cook & bring to a boil, stirring constantly so it does not scorch.
Sauce will become thick when it starts to boil.
Cook pasta while sauce is cooking. Do not overcook, leaving it `al dente`.
Combine sauce with pasta and crushed pineapple. Refrigerate overnight.
Add Mandarin oranges (cut up into smaller pieces) and Cool Whip just before serving. Mix thoroughly.